Various materials are known for use in the packaging industry. The various properties sought in such materials include attractive appearance and enhanced barrier to ultraviolet and visible light, as well as to moisture, oxygen and aroma.
Among such materials are the metallized films. Suitable polymers for these films include the polyolefins such as polypropylene. Commercially available metallizable films are described in Hercules Incorporated Technical Information Bulletins FC-33B and FC-47A. These products consist of an Opaque homopolypropylene core provided with a metal coating receiving layer to which has been added a hydrocarbon resin as a processing aid as well as other additives including slip agents and antiblock agents. The polypropylene core is opacified by inclusion therein of a particulate material that leads to the formation of internal voids in the polymer matrix when the film is drawn. These films, for reasons that have not been fully explained, exhibit very poor metal adhesion and are accordingly useful for only relatively low performance applications such as candy wrappers and insulation facing.
The inclusion of different additives, blended with the polyolefins, is also known. For instance, TORAY INDUSTRIES,INC. (Japanese Patent Publication No. 61-225049) discloses various films of polypropylene blended with petroleum and/or terpene resins and metallized with aluminum.
Particularly, the invention to which this reference is directed involves corona treatment of polypropylene film surfaces under nitrogen and carbon dioxide atmospheres. This treatment introduces imino and/or amino nitrogen groups into the surface to a depth of 100 Angstroms. It is the thusly treated film surface which is metallized.
TORAY INDUSTRIES, INC. also discloses comparative examples. One of these, Comparative Example 3, discloses corona treatment of a polypropylene surface in the presence of air with the previously discussed introduction of nitrogen accordingly not taking place. Metal is thereafter deposited on this surface. The resulting film is indicated to have a Moisture Permeability Rate, measured at g/m.sup.2 /day/15 .mu.m, of 2.1.
It has been discovered that transparent films with at least one polyolefin layer and, further, having a barrier coating receiving surface can be provided wherein such surface is characterized by a topography--specifically, a consistent roughness--not previously known or suggested in the art for such films. It has also been discovered that such films, of the indicated topography, possess a degree of moisture and oxygen barrier also not known or suggested in the art. Moreover, they exhibit both excellent resistance to metal cracking and superior metal adhesion.
Yet additionally, it has been discovered that polyolefin films, likewise with the indicated one or more polyolefin layers wherein the barrier coating receiving surface is provided by a polyolefin layer and wherein this layer includes a hydrocarbon resin can be provided with the indicated advantageous properties.
It has also been discovered, as to such polyolefin films, that the barrier coating receiving surface provided by the indicated polyolefin layer can likewise be characterized by an increased resistance to damage from contact with other surfaces.
Still further, it has been discovered that composite, or multilayer polymer films, including both a core layer and a polyolefin barrier coating receiving layer, can be provided, with the barrier coating receiving layer including a hydrocarbon resin. Consistent with the foregoing, such films similarly exhibit excellent barrier properties, resistance to crazing and metal cracking and superior metal adhesion.